Biology Lecture 3: Body Size and Allometry

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Questions and Answers

What does the term 'allometry' specifically imply regarding an animal's anatomical features?

The animal's proportions change consistently with alterations in its size. (correct)

The animal's proportions remain constant as its size changes.

The animal's proportions exhibit stochastic variations irrespective of changes in size.

The animal's proportions remain constant only for certain life stages.

Given the formula for Basal Metabolic Rate (BMR) as $M = aW^b$, what does 'b' represent?

The animal's total body mass.

The animal's metabolic rate at its maximum.

The mass exponent controlling the relationship between mass and metabolic rate. (correct)

A constant related to the species of the animal.

What characterizes isometry with changes in size?

The proportions within the animal remain the same whether the animal shrinks or grows. (correct)

Isometry refers to the mass-specific metabolic rate, not anatomical proportions.

The proportions within the animal change disproportionally as the size increases.

The proportions of the animal vary due to external environmental pressures.

How does plotting data on log axis scales help in the study of allometry, using the BMR formula $M=aW^b$ as an example?

It transforms the power relationship into a linear one, simplifying analysis. (C) Signup and view all the answers

Which of the following correctly represents the concept of physiological allometry?

An animal's physiological processes change disproportionately with its size. (C) Signup and view all the answers

What physiological constraint prevents the pygmy shrew's heart from beating at its predicted rate based solely on its mass?

The inherent contractile speed of cardiac muscle limits how quickly it can contract and relax. (B) Signup and view all the answers

Based on the scaling relationship for heart rate and mass in mammals provided (Heart rate = $241M^{-0.25}$), what prediction would be made for a mammal with a smaller mass?

A higher heart rate. (A) Signup and view all the answers

Given the data presented, where does the pronghorn fit in relation to general mammalian trends?

The pronghorn’s heart rate is much higher than predicted given its size, therefore classifying it as an exception. (A) Signup and view all the answers

How does the scaling exponent of lung mass compare to the scaling exponent of VO2max in mammals?

Lung mass has a significantly higher exponent than VO2max. (C) Signup and view all the answers

What explanation does the text suggest for why lungs do not scale directly with aerobic capacity in mammals, unlike most other components of aerobic metabolism?

Lungs serve multiple functions beyond oxygen uptake, which influences their scaling. (A) Signup and view all the answers

What does the variable 'b' represent in the equation log M = log a + b log W?

The slope of the logarithmic equation (D) Signup and view all the answers

In the equation BMR = 70M^0.72, what does the constant 70 represent?

The baseline basal metabolic rate (A) Signup and view all the answers

Why do small animals require a higher metabolism relative to their size according to the discussed principles?

They have a larger surface area compared to their volume. (A) Signup and view all the answers

What is the approximate value of the mass exponent 'b' for maximal metabolic rate (VO2 max) scaling in elephants?

0.86 (A) Signup and view all the answers

What scaling principle often requires novel adaptations in mammals?

Heart mass scaling (B) Signup and view all the answers

What aspect of ectotherm metabolism scales similarly to the mass exponent seen in thermoconformers?

Scaling of metabolic rates (C) Signup and view all the answers

Which factor does not directly influence mass-specific allometry equations?

Body temperature regulation methods (B) Signup and view all the answers

Which equation reflects the relationship between mass (M) and weight (W) involving a mass exponent?

M/W = aW^(b-1) (D) Signup and view all the answers

Study Notes

Lecture 3: 10 Jan

Lecture topic: Body size, allometry, and physiological allometry, causes, exceptions, correlates, and implications.
Reading assignments: Pages 19-20, 184-192, 230-233

Scope of Animal Size

How small?
How big?

Scope of Invertebrate Size

How small?
How big?

Scope of Mammal Size

How small?
How big?

Scope of Bird Size

How small?
How big?

Patterns of Size Change: Isometry

Proportions remain the same with changes in size.

Patterns of Size Change: Anatomical Isometry

Proportions remain the same with changes in size, exemplified by animals like salamanders and fish.

Patterns of Size Change: Anatomical Allometry

Proportions change with size, like in human development from newborn to adult.

Physiological Allometry: Linear Axis Scales - Basal Metabolic Rate (BMR)

Basal metabolic rate (BMR) is proportional to body weight raised to a power (M = aWb).
The mass exponent (b) is approximately 0.72–0.73.
This relationship is not consistent across all species.

Log Axis Scales & Allometry: BMR

Plotting the log of metabolic rate against the log of body mass yields a linear relationship.
The slope of this line (b) is the scaling exponent (approximately 0.72).
The intercept (log a) relates to the proportionality constant.

Mass-Specific Allometry: BMR/g

The metabolic rate per gram of body weight (M/W) scales with body weight raised to a power (b-1).
The scaling exponent (b) for BMR/g is approximately -0.28.

Log Scales & Mass-Specific MR

The log of metabolic rate plotted against log of body mass yields a linear relationship.
The slope (b) is around 0.71.

What "Causes" Metabolic Allometry?

Heat production within animal volume and exchange with environment are factors influencing metabolism.
Smaller animals lose heat rapidly relative to their surface area, needing higher metabolisms to compensate.
The relationship between SA/V and metabolic scaling is not consistent across all animals.
Other factors like ectothermic metabolism scaling differ (around 0.75).

Ectotherm Scaling

Ectothermic organisms (cold-blooded) have different metabolic scaling relationships compared to endotherms (warm-blooded).

Scaling of Maximal Metabolic Rate (VO2 max)

The maximal metabolic rate scales with body mass raised to a power (b), approximately 0.86.
The relationship is different for domesticated animals vs. wild.

Measuring VO2 max

Various methodologies, including experiments on animals and humans, are used for this measurement.

Scaling Constraints & Adaptations

Scaling constraints often require novel adaptations.
Mammalian heart mass and rate scaling follow different relationships.
Pygmy shrews have high heart rates, exceeding the theoretical maximum from scaling relationships.

Mammalian Cardiac Scaling

Comparing heart mass and heart rate to metabolic rates shows exceptions to general scaling rules.

Informative Exceptions

Animals like pronghorn buck deviate from the typical scaling relationship of body mass and metabolism.
Several factors, including adaptations for activity levels, contribute to these deviations.

Informative Exceptions (2)

Allometry of components of aerobic metabolism in mammals is similar to VO2max principles.
Lungs exhibit scaling patterns differing from general aerobic metabolism trends.

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Description

Explore the intricacies of body size, allometry, and physiological allometry in this engaging quiz. Delve into the factors influencing animal size, including anatomical isometry and allometry, and understand their implications across various species. This lecture addresses key concepts regarding size changes in invertebrates, mammals, and birds.